Gaseous discharge ballast



Dec. 17, 1963 P. BERGER 3,114,861

GASEOUS DISCHARGE BALLAST.

Filed Oct. 17, 1960 2 Sheets-Sheet 1 IN VEN TOR.

j wfgeger BY SEW MMQQ Dec. 17, 1963 P. BERGER 3,114,861

GASEOUS DISCHARGE BALLAST Filed 001;. 17. 1960 2 Sheets-Sheet 2 IN V EN TOR.

This invention relates generally to gaseous discharge ballasts, and more particularly is concerned with a type of ballast in which the laminations which form the core of the ballast are made with a minimum of scrap. lmportantl-y the invention is also concerned with a novel ballast in which the core of the ballast has a novel configuration resulting in certain advantages to be enumerated.

As well-known, gaseous discharge devices such as the popular fluorescent lamps which are commonly used for lighting purposes require substantially higher voltages for ignition than for operation. In order to supply the voltages from alternating current sources, apparatus normally are provided which serve several purposes including (a) the raising of the line voltage to ignition voltage by transformation, ([7) the automatic lowering of the voltage after ignition to operating value and (c) the provision of means to limit the flow of current through the gaseous discharge device after ignition.

All of these functions mentioned are usually provided by means of a transformer which has substantial leakage reactance deliberately built thereinto. 011 open circuit when the discharge device is not ignited its impedance is substantially infinite, and the flow of current in a primary applied to a suitable secondary winding, either by autotransformation or straight transformer action will depend to a great extent upon the turns ratio with little regard for leakage reactance because there is no current flowing in the secondary winding. The high voltage generated is sufficient to ignite the gaseous discharge device causing the low pressure gas contained within the envelope to ionize and commence to pass current. As soon as current commences to flow in the secondary winding, the leakage reactance is felt and the impedance produced in the secondary thereby places a limit on the amount of current that can flow while decreasing the totalvoltage across the gaseous discharge device.

Such apparatus has come to be known as a ballast although its ballasting function is only one phase of the work the device is called upon to perform. Designers skilled in this art are able as a rule to work out the physical characteristics of ordinary ballasts for meeting the requirements of known lamps, notwithstanding the fact that the phenomena occurring in electromagnetic circuits of this type are not fully understood. Experience has pro vided certain information, both arbitrary and logical, upon which the normal design procedure is based.

his invention is concerned with a ballast of the kind in which there is a leading current flowing in a secondary winding, posing problems of saturation and wave shape which have plagued designers for years. The primary problem in such ballasts has been providing high efiiciency in the operation of the apparatus and providing at the same time high lighting e'lliciency. Added to the principal problem are factors which complicate the situation and these are providing an economical ballast, providing a small cross section ballast, and providing a ballast which is simple in construction.

Reference is made to Feinberg-Endo Patent 2,892,249 owned by the assignee of this application which describes a novel method of forming the laminations of a ballast in which there are provided a T-shaped center winding leg and a pair of l---shaped side legs facing the T-shaped center leg so that the central extensions of the F-shaped nited States Patent 0 angst side legs form a shunt between windin s which are located on opposite sides thereof.

The core which is formed by the method of said Patent 2,892,249 is of the so-called shell variety and the ballast which resulted was intended especial-1y, although not so limited, for use with a type of apparatus known as a series-sequence circuit. In stamping the laminations from which the stacks forming the core were made, the F-shaped laminations were cut with the elongate portion of a shaped element having its opposite edges common with the inwardly facing edges of the contiguous F-shaped elements. The formation of the center extensions on the F-shaped elements thus notched into the sides of the T-shaped element. It was found that such a structure was satisfactorily usable in a ballast in which the reduced section of the T-shaped element would have little or no effect on the characteristics of the ballast.

Thus, as explained in said patent, the ballast was formed by stacking laminations to form portions of a core, after which assembly was accomplished by shifting the T-sllaped portion lengthwise of the two F-shaped portions so that the notches were not aligned with the shunt-forming extensions, although the two shunt forming extensions were aligned on opposite sides of the central winding leg. The structures with which such a core was especially intended was that described in US. Patents 2,55 8,293 and 2,683,243. These structures are the so-called series-sequence devices in which there is a high reactancc secondary winding that carries very little if any current during operation of the device. Thus, if the notches resulting from the formation of the shunt extensions were placed beneath this high reactance secondary winding, it was found that there was no practical effect upon the wave shape.

Where used in a series-sequence ballast of the type mentioned in the manner described, therefore, the notches in the central winding leg served no advantageous function.

In the invention herein it has been found that if the teachings of the said Patent 2,892,249 are applied to a series-sequence ballast of the so-called rapid-start type, certain unobvious and highly advantageous results are additionally achieved.

The primary object of the invention therefore is to provide a ballast in which the core is manufactured by the method of Patent 2,892,249 but in which the notch resulting from the removal of metal from the central winding leg is utilized to produce a more efiicient and highly desirable ballast structure.

Still a. further object of the invention is to provide a novel ballast structure in which there is a bridge gap adjacent a shunt whereby to enable economical manufacture of the ballast and efiicient and desirable operation thereof.

Further objects of the invention are concerned with the provision of a novel ballas structure which, although the ballast is highly economical to manufacture, has a very low crest factor with resulting increase in lighting efiiciency, has low currents and low losses; the provision of a ballast in which the inductance of the circuit can be easily and simply varied for most economical condenser requirements.

Many other objects of the invention will occur to those skilled in this art as a description of the details thereof proceeds, in connection with which there are illustrated and described preferred embodiments in the accom .ying drawing. Where feasible the same characters i reference are used throughout the several figures to designate the same or equivalent elements or parts.

In the drawings:

FIG. 1 is a diagrammatic top plan view of a transformer constructed in accorda c-e with the invention and using the novel core thereof, the coils of the apparatus being shown in section.

FIG. 2 is a fragmentary top view of a strip of electrical steel showing the layout of parts of the core of FIG. 1 along the same in order to illustrate the manner of forming the laminations which make up the core.

FlG. 3 is a circuit diagram of the ballast of the invention utilizing the transformer of FIG. 1.

FIG. 4 is a chart showing the approximate wave shape of the current flowing in the ballast and applied to the lamps for operating the same.

PEG. 5 and FIG. 6 are views similar to that of PEG. 1 but of modiied forms of the invention.

The invention herein is characterized by the provision of a ballast having a. core that is formed by the method which is described in said Patent 2,892,249, but in which the notches which result from the removal of the metal which form the shunts are disposed under a secondary winding which carries a leading current. T his arrangement has been found to provite nany advantaces, primarily of which ar high lighting elhciency, low current, and stability or good regulation.

Attention is invited to H6. 3 for a. circuit diagram of the circuit with which the invention is especially intended to be so FIG. 3 illustrates a so-callcd rapid-start circuit in which the lamps L and L are of the rapidstart variety, having filaments (not shown) which carry current continuously throughout the operation of the apparatus. The circuit of 3 is well-known and con ventional in every respect except one which will be mentioned. There is a primary winding P which is connected by the leads T2 and 14 across a source of AC. power, such as, for example, a conventional 120 volt line. The terminals of the primary winding P are designated l6 and The terminal 18 forms a juncture between the primary winding l and a secondary winding S. The right-hand terminal of the winding S is connected through a capacitor C by way of the conductor 2%- to the lamp L so that the capacitor C is a series element.

This capacitor provides power factor correction while the lamps are in operation, and hence, it will be obvious that the secondary winding S will be carrying a leading current while the apparatus is in use. The left-hand terminal lb of the primary winding P is connected by way of the lead 22 to the left-hand terminal of the lamp L and the lamps L and L are connected in series by means of a jumper 24 so that, in effect, the primary and secondmy windings P and S are connected in autotransformer relationship and across both of the lamps L and L in series.

A shunting condenser C is connected across the lamp L so that upon energization of the primary winding P from the line the entire voltage generated by the primary and secondary together will be applied across the lamp L to light the same. Thereafter, when current flows in the lamp L this current passing through the condenser C will produce a voltage across the lamp L sufficient to ignite the same. When both lamps are in operation, the condenser C is bypassed through the lamp L and the entire circuit is, in eflcct, a cries circuit although the lamps are ignited in sequence.

There are three filament windings F F and F which are connected across the various filaments of the lamps. The winding F may be an extension of the primary winding P formed by means of a tap which comprises the junction 16, and it connects across the left-hand filament of the lamp L through the conductors 22 and 2s. The right-hand filament of the lamp L and the loft-hand filament of the lamp L are connected in parallel by means of the jumpers 24 and 2d, and these filaments are served in parallel by the filament winding E; which is closely coupled to the primary winding P and applied across the jumpers 2d and 28 by means of the leads 3%. The third filament winding F is also closely coupled with the primary winding P and it applies current across righthand filament of the lamp L by way of the Q2.

The windings are all mounted upon a core to form what may be designated transformer 34, including certain elements or members which will be described and having a shunt 36 between the windings P and S in order to provide the desirable and necessary leakage reactance. In order to illustrate that there is a reduced section in the core of the transformer 34 adjacent the shunt, the rectilinear lines, usually drawn parallel conventionally to illustrate a core, are shown as having a break therein at 38. This will be described in detail.

FIG. 1 illustrates a transformer 34 constructed in accordance with the invention. The transformer core is made up of three stacks of laminations, which may be designated as a T-shaped central leg 49 and F-shaped side legs .2. The individual laminations from which the stacks are built up, preferably are stamped from continuous strips of steel with the elements mated or nested so as to provide a minimum amount of scrap. A layout along a strip of steel is shown in FIG. 2, and the manner in which the stamping or punching occurs is described in said Patent 2,892,249. For purposes of explanation, the reference character ill is applied to the T-shaped 1amination and the reference character to the F-shaped lamination. In the said Patent 2,892,249, the F-shaped laminations 42 were referred to as L-shaped laminations, but the structures are equivalent. In this specification, the laminations will be referred to as F-shaped, since this is the designation by which such laminations have become known in the trade.

Referring once more to FIG. 2, it will be seen that in the stamping process a pair of F-shaped laminations are nested on opposite sides of the T-shaped lamination so that the long inner edge of each of the F-shaped laminations is common with the long outer edge of the T-shaped lamination. Pairs of F-shaped laminations are arranged back-to-back, and the configuration is repeated. Thus, there will be two F-shaped laminations for each T-shaped lamination with very little resulting scrap. The scrap resulting from this process is designated by the reference character S and is cross-hatched. Some of the scrap is inevitable due to the notching of the corners of the F- shaped laminations for the securement of clamping members thereto, as will be explained.

Referring once more to FIG. 1, the T-shaped portion of the core of the transformer 34 has an elongate, central winding leg portion 4 3 and a left-hand bridging portion 46 which is the cross-head of the T. The F-shaped portions 42 of the core of the transformer 34 provide the elongate, parallel side legs 43, inwardly directed end extensions 59, and center inwardly directed extensions 52 which are of such transverse (vertical in FIG. 1) dimension as to provide appropriate air gaps at 54 so that the portion of the transformer 34 which is at that location comprises shunt 36 between the right and left-hand portions of the transformer. The notch resulting from the removal of the metal from the extension or lugs 52 is designated 38, and the central winding leg 44 thereby is provided with a reduced cross-section at as. Due to the configuration of the parts, there are formed windows 62 and 64 on opposite sides of the central winding leg 44. The ends of the cross-head 46 abut the inner edge of each of the side legs 48 at their left-hand ends, as shown at 66, while the inner extensions 50 abut the opposite side edges of the central winding leg 41-4 at the right-hand end thereof as shown at 6%. The primary winding P and the filament windings F F and F are all disposed in the windows 62 and wound around the central winding leg 44 thereat, while the secondary winding S is disposed in the window 64 and wound around the central winding leg 44 thereat. Normally these windings are preformed on suitable rectangular paper tubing and are slipped over the stacks of accommodate clamping members '72 which hold the entire transformer 34 in assembly. The clamping members 72' are merely shown in symbolic form.

Considering the dimensions of the various elements of the transformer 3d, in effect, when assembling the parts, the F-shaped parts 42 are shifted to the left relative to the T-shaped part 4%) from the disposition shown in FIG. 2 to the disposition shown in FIG. 1, while at the same time moving the same outwardly relative to the T-shaped portion This means that the distance from every point of the inward extensions 52 measured along the horizontal to the corresponding point of the notch 33 will be the amount by which the F portions 12 were longitudinally shifted. This dimension is equal also to the horizontal thickness of the inward extensions 50 and the cross-head 46. in other words, the dimensions X, Y and Z in FIG. 1 are all substantially equal.

The dimensions and physical characteristics of the transformer 34 connected in the circuit of FIG. 3 will be described hereinafter, but for the purposes of describing the results achieved, reference will be made to the use of the circuit of FIG. 3 with two 40-Watt rapid-start lamps. The conventional 40-watt lead-type, rapid-start ballast normally requires that approximately 430 milliarnperes of current be drawn in order to obtain 106% light output. This assumes a fairly good sinusoidal Wave shape with a crest factor of approximately 1.41. Distortion can increase this requirement to as much as 450 milliamperes of current. Using a structure such as described and with suitable proportioning of the air gaps 554i and the width of the extensions 52, it was found that lamp current crest factors of the order of 1.35 were obtained. With such crest factor, 100% light output was achieved with only 400 to 410 milliamperes of current. The wave shape of such currents is shown approximately in FIG. 4. It will be noted that there is a rounded top and a broadening to the right of the peak which gives rise to such beneficial crest factors.

Another advantage which has arisen by virtue of the structure which has been described is that the width of the extension 52 and consequently the width of the bridged notches 38 may be varied to change the effective inductance of the secondary winding S. This enables a condenser of lower voltage rating to be used. For example, in a conventional ballast for rapid-start lamps, it was required that there be a 3.6 microfarad 33(l-volt condenser at C With the structure of the invention, a much more economical condenser was capable of being used. It was found that the condenser capacitance could vary from 3.8 to 4.1 with a peak voltage of 285 to 260.

A practical example of the invention was constructed in which the configuration was identical to that of 1. The overall length of the lamination 4% inches with the remaining dimensions proportional. transverse length of the extensions (from top to bottom) was .225 inch with a gap of inch. The total width of each. of the windows 62 and .310 inch. The width of the s legs was .350 inch, and the width of the central winding l-"l was .764 inch. The distance X, Y and F1 was .385 inch, and the length of the extension measured horizontally was .188 inch. The stack height was .800 inch. The primary winding had 790 turns of No. 26 gauge wire, and the filament windings were 26 and 29 turns. The secondary winding had 1455 turns of No. 27%. gauge wire. The condenser was 3.75 in-icrofarads.

lt found that on open circuit the secondary voltage m asured from the juncture 18 to the condenser C was 174- vo lts, and when measured from the juncture 16 t the condenser C the voltage was 291 volts. The secondary voltave increased to 225 volts during operation with the voltage across the condenser C at 27 5 volts. This shows that it was possible to use a. large capacitance with lower voltage rating.

Flux del .31 measurements rade indicated that there was considerable saturation, of order of 25,000

along {the reduced cross section 615 of the central winding leg 44 during operation. It is not known precisely what effect this had, although it was noted that variations in the line voltage resulted in current variations but with little or no detectable change in the light output of the lamps.

in FlGS. 5 and 6, there are illustrated two transformers designated 1% and M2. it may be assumed that the construction of these transformers and the circuits with which the same are used are substantially similar to the construction {of FIG. 1 and the circuit of PEG. 3. In each case, a bridged air gap is formed at 3%; from the removal of metal forming the shunt Ed. in each case, it is intended that the secondary winding S be required to carry either the main lamp current or a leading current. it will be obvious also that a circuit such as FIG. 3 need not have two lamps ibut may utilize only one, or it may use more than two. he invention will be applicable as Well to such circuits.

FIG. 6 is intended to illustrate a transformer 1 312. which has unusual length. Since the bridged gaps 3 8 are adjacent the shunt 36, the effects of leakage reactance at the remote right end of the transformer may require one or more gaps such as shown at T he invention contemplates and includes such structures.

It is believed that the invention has been sufficiently described such as to enable those skills in this art to produce and use ballasts utilizing the teachings thereof. The theories used to explain the operation of the apparatus may or may not be correct. These tlheOric-s at this time seem logical, but in any event, are posed only for the purpose of aiding in an understanding of the invention and the manner in which it is used and operated. Benelicial results which are described are obtained as a result of the structure set forth hereinabove and claimed hereinafter.

What it is do ired to secure by Letters Patent of the United States is:

1. A ballast structure for igniting and operating at least one gaseous discharge device from an AC. source, and which comprises a transformer having a core made up of a center T-shaped part and two outer nested F-shaped parts with the long legs of the parts spaced to provide winding windows, a pair of lateral lugs in the center of each F-shaped part extending across the space toward the long leg of the 'i-shaped part but each terminating short thereof to lform a gap whereby to form a shunt in the core thercat primary and secondary windings in transformer relation mounted on the long leg of the T-shaped part and disposed in the windows on opposite sides respectively of the shunt, a condenser, lead means for connecting the primary winding across source and at least the secondary winding in series with. the condenser and the discharge device whereby leadhig current will flow in she secondary winding during operation of the discharge device, a notch in each of the long leg of the T-s'haped under the secondary winding and adjuent each lug of a configuration and of dimensions substantially the on re as the configuration and dimensions of the said adjacent lug.

2. A structure as claimed in claim 1 in which the primary and secondary winding are in autotransforiner 'elationsihip.

3. A structure as claimed in claim 1 in which every point on each lug is spaced from the equivalent point on its adjacent notch by a distance measured along the length of the long leg of the T-shaped part which is substantially equal to the width of the cross-head of the said 'i"-shapet part.

4. A structure as claimed in claim 1 in which there is a bridged gap addi ionally in said T-shaped part under said secondary winding spaced from said notches.

5. Apparatus for igniting and operating at least one gaseous discharge device from an AC. source which cornprises a transformer having an iron core consisting of an 7 elongate T-shaped part formed of a cross-head and a center leg, and a pair of elongate F-shaped parts each formed of an elongate side leg and an end and central lateral extensions, the parts being disposed with the end lateral extensions facing one another and abuttingly sand-- wiching the center leg of the T-shaped part therebetween and the cross-head of the T-shaped part aligned with and abutting the ends of the F-shaped parts opposite the end lateral extensions, whereby to form at least two pairs of windows between the resulting parallel side and center legs, a primary winding mounted on the center leg disposed in one pair of windows and having lead means for connecting same to said source, a secondary winding in transformer relation and coaxial with said primary Winding and mounted upon said center leg disposed in said second pair of windows with the said central lateral extensions positioned between the windings to serve as a shunt, the transverse dimensions of said central lateral extensions being less than the width of said windows whereby to provide nonmagnetic gap means in said shunt, a condenser, said secondary winding having lead means for connecting said condenser and gaseous discharge device in series with at least said secondary winding whereby a leading current will flow through said secondary winding during operation of said discharge device, there being a pair of notches in said center leg forming a bridged gap therein under said secondary Winding adjacent said shunt, each notch being formed in an oppote edge and being of substantially the same configuration and dimensions as the adjacent central lateral extension.

6. Apparatus as claimed in claim in which the distance measured along the length of the core from any point of said central lateral extension to the equivalent point of its adjacent notch is substantially equal to the width of the end lateral extension also measured along the length of the core.

7. In a ballast structure for igniting and operating at least one gaseous diseharge device from an A.C. source, comprising an elongate iron core transformer formed of a central winding leg of T-shaped configuration, a pair of parallel side legs on opposite sides of the central winding leg of F-shaped configuration, the central lateral extensions of the side legs extend toward and terminate short of the central Winding leg to provide a shunt thereat, a primary and a secondary winding disposed respectively on opposite sides of the shunt, the windings being connected in transformer relationship, :a capacitor, at least the secondary Winding being connected in series with said capacitor and across said gaseous discharge device, whereby a leading current flows in said secondary winding; the invention herein which comprises, means providing substantially reduced crest fiactor in said gaseous discharge device which consists of a bridged gap in the central Winding leg beneath the secondary winding adjacent the shunt formed of a pair of transversely aligned notches on opposite respective edges thereof, said notches being of the same configuration and dimensions as the said centnal lateral extensions, whereby laminations for torming said legs may be punched in nested condition and thereafter separated with a minimum of waste.

8. A structure as claimed in claim 7 in which the distance between equivalent parts of the respective extensions and notches measured along the length of the transformer is substantially equal to the width of the crosshead of the T-shaped central winding leg.

9. Apparatus for igniting and operating a pair of gaseous discharge devices from an AC. source comprising a transformer core formed of a T-shaped central winding leg and a pair of oppositely arnanged F-shaped side leg a primary Winding and a secondary winding coaxial with the primary winding both mounted on the central winding leg with the center extensions of the F-shaped legs sepanating the windings and serving as shunt between windings, a condenser, the primary and secondary windings being in transformer relation, at least the secondary being connected in series with said capacitor and the two gaseous discharge devices and adapted to carry a leading current during operation of the discharge devices, a recess in each edge of the central winding leg adjacent each center extension, beneath the secondary winding, the extensions and recesses being substantially identical in configuration and dimensions whereby the laminations forming the winding leg and side legs may be punched, nested and then separated and stacked Without the need for substantial further processing.

10. Apparatus as claimed in claim 9 in which there is a shunting capacitor across one gaseous discharge device whereby the devices ignite in sequence b ut operate in series.

References Cited in the file of this patent UNITED STATES PATENTS 2,892,249 Feinberg et al. June 30, 1959 

9. APPARATUS FOR IGNITING AND OPERATING A PAIR OF GASEOUS DISCHARGE DEVICES FROM AN A.C. SOURCE COMPRISING A TRANSFORMER CORE FORMED OF A T-SHAPED CENTRAL WINDING LEG AND A PAIR OF OPPOSITELY ARRANGED F-SHAPED SIDE LEGS, A PRIMARY WINDING AND A SECONDARY WINDING COAXIAL WITH THE PRIMARY WINDING BOTH MOUNTED ON THE CENTRAL WINDING LEG WITH THE CENTER EXTENSIONS OF THE F-SHAPED LEGS SEPARATING THE WINDINGS AND SERVING AS SHUNT BETWEEN WINDINGS, A CONDENSER, THE PRIMARY AND SECONDARY WINDINGS BEING IN TRANSFORMER RELATION, AT LEAST THE SECONDARY BEING CONNECTED IN SERIES WITH SAID CAPACITOR AND THE TWO GASEOUS DISCHARGE DEVICES AND ADAPTED TO CARRY A LEADING CURRENT DURING OPERATION OF THE DISCHARGE DEVICES, A RECESS IN EACH EDGE OF THE CENTRAL WINDING LEG ADJACENT EACH CENTER EXTENSION, BENEATH THE SECONDARY WINDING, THE EXTENSIONS AND RECESSES BEING SUBSTANTIALLY IDENTICAL IN CONFIGURATION AND DIMENSIONS WHEREBY THE LAMINATIONS FORMING THE WINDING LEG AND SIDE LEGS MAY BE PUNCHED, NESTED AND THEN SEPARATED AND STACKED WITHOUT THE NEED FOR SUBSTANTIAL FURTHER PROCESSING. 